The present invention relates to a hydraulic pressure controller of a dual hydraulic braking system for vehicles, particularly for four-wheeled motorcars.
A known hydraulic pressure controller of this type incorporates a first pressure reducing valve and a second pressure reducing valve disposed in respective independent oil passages which connect a first output port and a second output port of a master cylinder with respective left and right rear wheel brakes, the first and second pressure reducing valves being adapted to transmit the output hydraulic pressures from the first and the second output ports to respective rear wheel brakes while proportionally reducing the pressure. The pressure reducing valves incorporate respective piston valves which are contacted at their one end by a balancing lever which in turn is urged by a common spring for determining the pressures at which the piston valves commence the pressure reducing action.
In the device described above, when proper oil pressures are maintained in two systems, both piston valves are operated overcoming the set load of the spring, in accordance with the rise of the output oil pressure of the master cylinder, so that the above-mentioned output pressure is reduced proportionally and transmitted to the left and right rear wheels. This prevents the locking of the rear wheels attributable to the reduction of the load on the rear wheels during braking.
In the above-described device, however, it is necessary to incorporate two expensive reducing valves. In addition, a complicated mechanism for attaining the balance of pressures for both rear wheels is required, so that the cost of the device as a whole is raised inconveniently.